Absorbent structure and an absorbent article which includes the absorbent structure

ABSTRACT

An absorbent structure in an absorbent article, such as a sanitary napkin, tampon, panty protector, incontinence guard, diaper and the like, which is produced by including in the absorbent structure a polymeric foam having cells which were initially essentially closed and which has been worked so as to open said cells, and the structure has obtained liquid take up properties. The foam has a density between 0.01-0.5 g/cm 3 . The material has porperties which are effective in achieving the function for which the product is intended. The foam may be formed as a sheet and the sheet can be made very thin and light, with a surface weight of between 10-500 g/m 2 , and the article will therefore exhibit good comfort properties to the wearer and requires only a small amount of material for its manufacture.

BACKGROUND OF THE INVENTION

The present invention relates to an absorbent structure in an absorbentarticle, such as a sanitary napkin, tampon, panty protector,incontinence guard, diaper and the like.

Many different types of absorbent articles of this kind are known to theart. The absorbent body of such products is conventionally produced bydry-defibering cellulose pulp in roll, bale or sheet form for instance,and converting the cellulose pulp in fluffed form to a pulp mat,sometimes admixed with so-called superabsorbents in the pulp mat, thesesuperabsorbents being polymers which are capable of absorbing many timestheir own weight of water or body fluid.

The pulp body is often compressed, with the intention of enhancing itsfluid-dispersion properties and also to lower the bulk of the pulp bodyand therewith to obtain a product which is as compact as possible.

The absorbent body may include other constituents, for instance toimprove the fluid-receiving properties or the liquid-dispersionproperties of the absorbent body, or to increase its coherency and itsability to resist deformation in use.

With the majority of sanitary products, it is desired that the articleshall be thin and pliable, partly to enable the article to be worn asdiscretely as possible and partly so that the article will feel ascomfortable as possible to the wearer. Another problem is the so-calledrewetting problem. By rewetting is meant that body fluid that hasalready been absorbed by the sanitary article is pressed back intocontact with the wearer's skin by external forces, for instance when thewearer sits down. It is a general desire that the surface of the articlewhich lies proximal to the user will remain as dry as possible.

With regard to absorbent articles, it is desired to reduce the amount ofmaterial in the article, so as to reduce commensurately the amount ofwaste that occurs when the used product is thrown away. It is alsodesired to enable the article to be manufactured from biologicallydegradable material.

Other problems concerning absorbent articles reside partly in theirtotal absorption capacity, and also in that the articles often leak longbefore their total absorption capacity has been utilized to the full.Among other things, this is because the discharged body fluid is unableto penetrate into the absorbent material and be dispersed to hithertounused regions of the article quickly enough, but instead leaks from thesides of the sanitary napkin, diaper or incontinence guard. The abilityof the materials used in such articles to disperse the absorbed fluidthrough-out the whole of the absorbent body is thus an important featureof such articles.

A very large part of the production plant employed in the manufacture ofsuch sanitary articles is normally comprised of defibrating equipment,pneumatic conveyor systems and mat-forming equipment. This equipmentoften constitutes serious source of error and faults in the productionplants. Additionally, this equipment is often followed by equipment forcompressing the finished pulp mat or the finished sanitary article.

EP 0,044,624 and U.S. Pat. No. 4,394,930, among others, describepolymeric foam having superabsorbent properties for use in absorbentarticles. The use in absorbent articles of polymeric foam which lackssuperabsorbent properties is described in EP 0,163,150 and EP 0,299,122,among others. Although these absorbent articles obtain good properties,the manufacturing process is relatively complicated and the materialsthus produced are relatively expensive.

U.S. Pat. No. 3,834,389 describes how a polyurethane foam, for instance,can be chemically reticulated in order to open up the common wallsbetween adjecent cell, which enhances the absorbancy of the foam.

OBJECTS AND SUMMARY

An object of the present invention is to provide an absorbent articlehaving an absorbent structure of the kind defined in the introductionwhich will afford a high degree of comfort to the wearer, among otherthings with regard to thinness and suppleness. It is also desired toreduce the amount of material consumed in manufacture. The article willpreferably have good absorbent properties and low rewetting tendencies.It is also desired that an absorbent article of the kind defined in theintroduction can be manufactured in a simplified manner. Thesedesiderata are satisfied by means of the present invention, in that theabsorbent structure includes a foamed polyolefin material having adensity of 0.01-0.5 g/cm³ and cells which are initially essentiallyclosed but which have been opened to increase the fluid take upproperties, e.g. the sorbing properties, of the material.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference toexemplifying embodiments thereof and also with reference to theaccompanying drawings, in which

FIG. 1 illustrates how the instantaneous absorption of the material isinfluenced by the number of times the material has been perforated byneedling;

FIG. 2 shows how instantaneous-rewetting and rewetting of the materialis influenced by the number of times that it has been perforated byneedling;

FIG. 3 shows how the instantaneous absorption of the material isinfluenced by its thickness, and also shows a comparison with areference product;

FIG. 4 shows how instantaneous-rewetting and rewetting of the materialis influenced by its thickness, and also shows a comparison with areference product;

FIG. 5 shows how instantaneous-rewetting and rewetting of the materialis influenced by the surfactant concentration of the solution used tosurface-modify the material;

FIG. 6 illustrates a comparison between instantaneous-rewetting andrewetting of an inventive material and various reference products;

FIG. 7 illustrates a comparison between instantaneous-rewetting andrewetting of an inventive material with and without SAP-tissue and areference product;

FIG. 8 is a top view of one example of an inventive absorbent article;the section A--A is shown in FIGS. 9 and 10;

FIG. 9 is a cross-sectional view of an example of the schematicconstruction of an absorbent article constructed in accordance with oneembodiment of the invention; and

FIG. 10 is a cross-sectional view of an example of the schematicconstruction of an absorbent article according to one embodiment of theinvention in combination with SAP-tissue.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As before mentioned, comfort properties, such as softness andsuppleness, and absorption properties such as absorption capacity,absorption rate and rewetting, are all important properties of amaterial used in the manufacture of a sanitary article. The fluidsconcerned include urine, menstruation blood, blood and wound fluids.

The object of the present invention is to provide an absorbent structurein an absorbent article, such as a sanitary napkin, tampon, pantyprotector, incontinence guard, diaper and the like, which will afford ahigh degree of comfort to the wearer, with regard to thinness andsuppleness among other things. Another object is to reduce the amount ofmaterial consumed in manu-facture. The material used in the article willalso preferably have good absorption properties and exhibit lowrewetting tendencies. A further object is to simplify the process ofmanufacture. A ready-to-use absorbent material in roll form which can beused without needing to defiber the material will eliminate therequirement of the aforesaid defibering equipment, pneumatic conveyorsystem and mat-forming equipment.

The aforesaid objects have been solved in accordance with the invention,by including in the absorbent structure a sheet which comprises a foamedpolymeric material having cells which were initially essentially closedand which have been opened so as to increase the fluid take upproperties of the material. The foam has a density of 0.01-0.5 g/cm³.

By perforating the foamed polymeric material by means of a needlingprocess, the material is given absorption properties which render saidmaterial highly suited for use as an absorbent material in the majorityof sanitary articles. Perforation of the material opens the cells in thepolymeric material which were initially closed, so as to form openstructures having fluid take up properties.

The material can be perforated mechanically by needling in the mannerused to produce needled felt for instance, or with the aid of water jetsunder high pressure in the manner used to obtain spunlace nonwovenmaterial.

The aforesaid methods of working the material shall be seen solely asexamples, and it will be understood that other methods can be applied toachieve corresponding results. An example of other conceivable methodsis one in which the material is perforated by electromagnetic radiationor with the aid of laser radiation.

The aforesaid polymeric foam has been found to provide a highlyefficient absorbent material and it has also been found possible to usethis absorbent material in sanitary articles. The foamed sheet can bemade very thin, therewith obviating the need to further compress theproduct. However, the sheet will permit further compression, if this isdesirable in respect of some product application. A suitable sheetsurface weight is 10-500 g/m².

The polymeric foam can be produced from both thermoplastic andthermosetting resins. The thermoplastics that can be used include simplepolyolefins, for instance polyethylene, which is an inexpensive andcommercially abundant material. The thermosetting materials that can beused include polyurethanes.

Foamed material can be produced from these plastics, for instance byblowing air into the molten plastic bath during manufacture, or byfoaming the material through fermentation by gas formation resultingfrom chemical reactions in the polymeric material.

When polyolefins are used to apply the invention, the absorbent articlecan be made very light in weight, and therewith economically beneficial.It is possible to reduce the weight of the absorbent body to 5-10% ofthe weight of a corresponding absorbent body made of conventionalcellulose material, while retaining the requisite absorption capacity ofsaid body.

The amount of waste represented by the absorbent article can also bereduced, by using bioplastics, which are renewable and biologicallydegradable. Examples of such materials are polysaccharide, polylactidesand polyhydroxy alkanoids, and mixtures of such polymers. Other types ofdegradable polymers can also be used.

When polyolefins are used to apply the invention, it is necessary tomodify the original hydrophobic surface to a hydrophilic surface. Thissurface modification can be achieved in different ways, for instance byadding surfactants, by plasma treatment, by corona treatment, bycopolymerization, by admixing other polymers, or by other methods. Whena surfactant is added to a material according to the invention, itsproperties can be adjusted with regard to absorption rate, absorptioncapacity, rewetting tendencies, etc.

A material according to the invention can be combined with conventionalabsorbent materials, for instance cellulose pulp, or with superabsorbentmaterial, to form an absorbent structure. An example of one suchmaterial is a so-called SAP-tissue which is comprised of two layers ofcellulose wadding with an intermediate layer of superabsorbent. Asuitable surface weight with regard to SAP-tissue is 50-100 g/m²,divided over two layers of cellulose wadding with a surface weight of10-20 g/m² and a layer of superabsorbent having a surface weight of40-80 g/m². Such an absorbent structure obtains an improvedinstantaneous absorption and better rewetting properties than anabsorbent structure having solely a polymeric foam according to theinvention.

Investigation of Material Properties

The following test methods and test equipment were applied to evaluatethe properties of the material.

Method 1--Determining Instantaneous Absorption

A sample body measuring 65×200 mm was punched from the material, weighedand then placed onto a flat supporting surface. 15 ml of sample liquid(0.9% NaCl-solution) was applied to the wetting point of the samplebody. The time taken to absorb all liquid was measured in seconds. Thistime period was expressed as instantaneous absorption.

Method 2--Determining Instantaneous Rewetting

A sample body measuring 65×200 mm was punched from the material, weighedand then placed on a flat supporting surface. 15 ml of sample liquid(0.9% NaCl-solution) were applied to the wetting point of the samplebody. A filter paper was then placed on top of the wetting point andsubjected to a load of 5 kPa for 15 seconds. The filter paper wasweighed before and after applying the load and the differencecalculated. The result, expressed in grams, was expressed asinstantaneous-rewetting.

Method 3--Determining Rewetting

This method was applied to determine rewetting after a load had beenapplied over a given time period. A sample body measuring 65×200 mm waspunched from the material, weighed and then placed on a flat supportingsurface. 15 ml of sample liquid (0.9% NaCl-solution) were applied to thewetting point of the sample body. A plexiglass plate having a largersurface than the sample body was then placed on top of the body andsubjected to a load of 5 kPa for 5 minutes. The plexiglass plate wasthen removed and a filter paper was placed on the wetting point andsubjected to a load of 5 kPa for 15 seconds. The filter paper wasweighed before and after subjecting the body to load and the result,expressed in grams, was expressed as rewetting.

Method 4--Manufacture of Sample Bodies for Determining the SurfactantInfluence

A sample body measuring 65×200 mm was punched from the material, weighedand then placed in a container containing an aqueous surfactant solutionfor 5 minutes. The sample body was then removed from the container andallowed to drain for 5 minutes, whereafter the sample body was subjectedto a load of 10 kPa for 5 minutes. The sample body was then dried in theabsence of load at a temperature of 40°-60° C. for 10-15 hours. Thesample body was then tested according to one of the Methods 1-3.

The Influence of the Needling Degree

Instantaneous absorption of a surfactant-treated polyethylene foamaccording to the invention, having a thickness of 4 mm, a surface weightof 80 g/m², and a density of 0.02 g/cm³, and which had been needled adifferent number of times was determined. The results were determined inaccordance with Method 1.

A Inventive material, needled twice.

B Inventive material, needled three times.

C Inventive material, needled four times.

It will be seen from FIG. 1 that material which had been needled threetimes had a slightly quicker instantaneous absorption than the remainingmaterials.

Instantaneous-rewetting and rewetting of a surfactant-treatedpolyethylene foam according to the invention having a thickness of 4 mm,a surface weight of 40 g/m² and a density of 0.02 g/cm³, and which hadbeen needled a different number of times was determined. The resultswere determined according to Method 2 and Method 3.

A Inventive material, needled twice.

B Inventive material, needled three times.

C Inventive material, needled four times.

It will be seen from FIG. 2 that instantaneous-rewetting and rewettingincreases slightly when the number of needlings are increased.

Influence of Material Thickness on Instantaneous Absorption

Instantaneous absorption of a surfactant-treated polyethylene foamaccording to the invention, having a density of 0.02 g/cm³, and whichhad been needled three times, was determined. The reference productcomprised a conventional cellulose pulp mat. The results are shown inFIG. 3. The results were determined according to Method 1.

A Pulp mat thickness 4 mm, density 0.12 g/cm³.

B Inventive material, thickness 2 mm.

C Inventive material, thickness 3 mm.

D Inventive material, thickness 4 mm.

It will be seen from FIG. 3 that material constructed in accordance withthe invention has quicker instantaneous absorption when the thickness ofthe material increases.

Influence of Material Thickness on Instantaneous-Rewetting and Rewetting

Instantaneous-rewetting and rewetting of surfactant-treated polyethylenefoams according to the invention having different thickness, 2-4 mm, anda density of 0.02 g/cm³, and which had been needled three times, wasdetermined. The reference product comprised a conventional cellulosepulp mat. The results are shown in FIG. 4. The results were determinedaccording to Method 2 and Method 3.

A Pulp mat thickness 4 mm, density 0.12 g/cm³.

B Inventive material, thickness 2 mm.

C Inventive material, thickness 3 mm.

D Inventive material, thickness 4 mm.

It will be seen from FIG. 4 that instantaneous-rewetting of inventivematerial increases slightly when the material thickness increases withinthe range of 2-4 mm. Rewetting is lower than rewetting of the referenceproduct, in all cases. It will also be seen that rewetting of materialconstructed in accordance with the invention decreases when the materialthickness increases within the range 2-4 mm. Rewetting is comparablewith or lower than with the reference product, in all cases.

Surfactant Admixture and Its Influence on Rewetting

Instantaneous-rewetting and rewetting of a surfactant-treatedpolyethylene foam according to the invention, having a density of 0.02g/cm³, and a thickness of 4 mm, and which had been needled three timesand treated with surfactant solutions of various concentrations is shownin FIG. 5. The samples were manufactured in accordance with Method 4,and the results were determined according to Method 2 and Method 3.

A Inventive material, 0.1% surfactant solution.

B Inventive material, 0.25% surfactant solution.

C Inventive material, 1% surfactant solution.

D Inventive material, 5% surfactant solution.

It will be seen from FIG. 5 that instantaneous-rewetting and rewettingdecreases when the surfactant concentration increases within the rangegiven.

Rewetting Compared with Conventional Products

Instantaneous-rewetting and rewetting for a surfactant-treatedpolyethylene foam according to the invention, having a density of 0.02g/cm³, a thickness of 4 mm, and which had been needled three times, andalso for conventional pulp pads were determined according to Method 2and Method 3. The conventional products comprised differentcellulose-fibre pulp mats. The results are shown in FIG. 6.

A Pulp mat thickness 10 mm, density 0.08 g/cm³.

B Pulp mat thickness 4 mm, density 0.2 g/cm³.

C Material constructed in accordance with the invention.

It will be seen from FIG. 6 that the instantaneous-rewetting andrewetting values of the inventive material are comparable with or lowerthan with the reference products. Reference 2 has the bestinstantaneous-rewetting value, while an inventive material has the bestrewetting value.

Rewetting of an Absorbent Body Incorporating SAP-Tissue, as Comparedwith Conventional Products

Instantaneous-rewetting and rewetting of a surfactant-treatedpolyethylene foam according to the invention, having a density of 0.02g/cm³, a thickness of 4 mm, and which had been needled three times andtested with and without the inclusion of SAP-tissue and of aconventional pulp pad were determined according to Method 2 and Method3. The SAP-tissue was comprised of two layers of 15 g/m² cellulosewadding and an intermediate 40 g/m² layer of superabsorbent. Theconventional product comprised a pulp mat of cellulose fibres. Theresults are shown in FIG. 7.

A Pulp mat thickness 10 mm, density 0.08 g/cm³.

B Inventive material, 4 mm without SAP-tissue.

C Inventive material, 4 mm+70 g/m² SAP-tissue.

It will be seen from FIG. 7 that inventive material which includedSAP-tissue exhibited better instantaneous rewetting values and rewettingvalues than the reference product.

Density and Surface Weight

The material can be made very thin, down to a thickness of about 1 mm,and consequently it is unnecessary, in many cases, to further compressthe material prior to its use in an absorbent article. A suitabledensity is 0.01-0.5 g/cm³, preferably 0.01-0.2 g/cm³, and morepreferably 0.02-0.1 g/cm³. A suitable surface weight is 10-500 g/m²,preferably 20-200 g/m² and more preferably 40-100 g/m².

Description of an Exemplifying Embodiment

FIG. 9 is a cross-sectional view of an inventive sanitary napkinaccording to a first embodiment. The napkin includes, conventionally, anabsorbent body 11 which is enclosed between a liquid-permeable top sheet12, which is suitably comprised of perforated plastic film, nonwovenmaterial or like material, and which lies proximal to the wearer in use,and a liquid-impervious bottom sheet 13. The sheets 12 and 13 have partswhich extend beyond the absorbent body 11, and are mutually joined atthese parts. The bottom sheet 13 is comprised of a suitable plasticmaterial, for instance polyethylene. Naturally, the top sheet and thebottom sheet may be formed from other known materials, within the scopeof the invention.

The absorbent body 11 consists solely of one single layer. This layermay be comprised of inventive material and optionally 0-10%superabsorbent material. A suitable density range with regard to theabsorbent body 11 is 0.01-0.1 g/cm³, while a suitable surface weight is20-100 g/m².

FIG. 10 is a cross-sectional view of a sanitary napkin according to asecond embodiment of the invention, this embodiment differing from theembodiment illustrated in FIG. 9, in that the absorbent body 21 includestwo layers 24 and 25. The layer 24 may be comprised of materialaccording to the invention, and optionally also 0-10% superabsorbentmaterial. The layer 25 may be comprised of so-called SAP-tissue, whichconsists of two layers of cellulose wadding, about 15 g/m², and a layerof superabsorbent material, about 40 g/m², placed between said twolayers of cellulose wadding. A suitable density range with regard to thelayer 24 is 0.01-0.1 g/cm³, while a suitable surface weight is 20-100g/m².

It will be understood that the invention is not restricted to thedescribed and illustrated exemplifying embodiments thereof and thatother embodiments are conceivable within the scope of the concept of theinvention.

I claim:
 1. An absorbent article, comprising:an absorbent structure, theabsorbent structure consisting solely of a foamed polyolefin materialhaving a density of 0.1-0.5 g/cm³, and cells of said foamed polyolefinmaterial that initially were closed have been opened by mechanicaltreatment to increase fluid take up properties of the material; aliquid-permeable top sheet; and an essentially liquid-impervious bottomsheet; wherein the absorbent structure is enclosed between saidliquid-permeable top sheet and said essentially liquid-impervious bottomsheet.
 2. The absorbent article according to claim 1, wherein saidstructure has the form of a sheet having a surface weight of 10-500g/m².
 3. The absorbent article according to claim 1, wherein thepolyolefin material includes 0.1-25 percent by weight of surfactant. 4.The absorbent article according to claim 1, wherein the polyolefinmaterial includes 1-50 percent by weight of superabsorbent material. 5.The absorbent article according to claim 1, wherein the structureincludes a separate layer of some other absorbent material.
 6. Theabsorbent article according to claim 5, wherein the separate layer ofabsorbent material includes cellulose and superabsorbent material. 7.The absorbent article according to claim 1, wherein said structure hasthe form of a sheet having a surface weight of 20 to 200 g/m².
 8. Theabsorbent article according to claim 1, wherein said structure has theform of a sheet having a surface weight of 40 to 80 g/m².
 9. Theabsorbent article according to claim 1, wherein said treatment has beeneffected by perforating the polymeric material by needling.
 10. Theabsorbent article according to claim 1, wherein the treatment has beeneffected by perforating the polyolefin material with the aid of waterjets.
 11. The absorbent article according to claim 1, wherein thedensity is 0.01-0.2 g/cm³.
 12. The absorbent article according to claim1, wherein the density is 0.02-0.1 g/cm³.
 13. The absorbent articleaccording to claim 1, wherein the foamed polyolefin material ispolyethylene.
 14. The absorbent article of claim 1, wherein theabsorbent article is one of a diaper, sanitary napkin, tampon, pantyprotector, and an incontinence guard.